Location services are widely available and used. Many applications in a modern mobile phone can make use of the information relating to the location of the device in order to provide a for better user experience, for example by allowing data traffic offload, navigation, information about available nearby services, etc. In addition, this location information can usefully be shared with other devices.
Proximity Services (ProSe) is a new feature standardized by 3GPP providing services for ProSe-enabled UEs (User equipment) in proximity of each other. These features are standardized in 3GPP TS 22.278 (versions 13.3.0 published on 24 Jun. 2016) and TS 23.303 (version 13.4.0 published on 22 Jun. 2016). ProSe features include ProSe discovery and ProSe direct communication.
ProSe discovery is a process that allows ProSe-enabled UEs that are in proximity of each other to identify each other. ProSe direct communication enables the establishment of communication paths between ProSe-enabled UEs in direct communication range using E-UTRAN or WLAN.
This is a type of location service that is not directly based on the locations of the UEs, but rather is based on the ability of the UEs to detect each other's presence within the range of the service.
It has been proposed that ProSe discovery messages should include location information for security reasons. The transmitting device can generate the location information, and can then either include that location information explicitly in the communicated messages, or can use that location information in generating a Message Integrity Code (MIC) to be transmitted in the communicated messages. Several positioning systems have been standardized for LTE. Assisted GPS (A-GPS) is designated as the primary method while Enhanced Cell Identity (E-CID) and Observed Time Difference Of Arrival (OTDOA) are fall back ones. A-GPS requires a fix from 4 satellites which could be difficult in cities and indoor environments. OTDOA and E-CID are less accurate and require network coverage. Nevertheless, they work better where A-GPS fails and do not require as much power. WiFi positioning methods can also help indoors.
The inaccuracy levels of the methods above are in the worst case of the order of hundreds of metres (300 m). For Cell ID based methods, the inaccuracy varies up to the order of kilometres in rural areas. But because they are as power efficient as E-CID and OTDOA, these methods could also be used whenever such inaccuracy levels are tolerated.
However, such possible inaccuracies are often ignored when the device uses the location information.
In the context of Cellular Internet of Things (CIoT) applications such as in wireless sensors, there might be stringent requirements on power consumption so that the use of GPS sources is not possible as it incurs a huge drain on the device's battery. For the same reasons, processing overhead is to be minimized.
In the context of device to device, machine type communication, narrow band IoT (Internet of Things) or any other type of wireless communication where there are limited radio resources, including the location information might be considered as a waste of spectrum if its size is not negligible compared to the amount of data transferred.
For grid based approaches, other issues may arise related to the fact that the distance covered along the latitude lines, for a fixed longitude interval (e.g. 1 degree), depends on the latitude and basically decreases when moving from the equator towards the poles. As a consequence, the grid cells do not cover equally sized geographical areas.
There are other standardized grids where cells cover equally sized areas such as HEALPix. However, the resulting calculations related to coordinate conversion and cell identification are complex and will induce a considerable processing overhead.
3GPP discusses in 3GPP TR 33.833 V1.7.0 a security problem called the Spatial Replay for ProSe Direct Discovery. A spatial replay is caused by an attacker who listens to an air interface, collects discovery messages, and broadcasts them in a remote location which normally would be “out of range for ProSe”. Thus UEs might discover each other and keep on communicating, believing that they are in proximity of each other even though they might be far from each other and even in different mobile networks.